Current thickness and dielectric constant scaling remain a difficult challenge for future copper (Cu) capping/etch stop technologies and there are tradeoffs between density, which improves barrier properties, and dielectric constant, which increases with density. Difficult challenges include identifying materials with good adhesion to the low-dielectric constant (low-k) interlayer dielectric (ILD) and Cu, Cu out diffusion and H2O2/O2 in diffusion prevention, electromigration and leakage, and compatibility with Cu interconnect processing such as ILD etch, photoresist ashing, etc.
The scaling of current low-k SiCN and SiCO capping layer technologies are expected to continue; however, research is needed on the feasibility of monolayer thick capping layers with a dielectric constant of <4.0, since current SiN/SiCN/SiCO materials are expected to fail at these dimensions. Another high potential impact research challenge is the elimination of the dielectric capping layer/etch stop layer by implementing selectively deposited metallic capping layers (such as cobalt metal) or self forming CuSiN barriers. Also, initial investigation of self assembled monolayers (SAMs), as the top side capping layer, has been demonstrated to reduce surface oxides, and curtail in-plane Cu transport and electrical leakage. But, the best results with amino-phenyl terminated SAMs represented only 50% of the leakage performance of a SiN capping layer.
Additionally, to warrant potential solution consideration, more research is needed to address several challenges related to SAMs as top side Cu capping layers, which include: low-k ILD deposition compatibility (thermal stability, plasma damage, etc.), Cu/low-k ILD and top side low-k ILD adhesion, diffusion barrier performance to Cu and O2/H2O diffusion, and compatibility with interconnect processing (wet/dry etch, CMP, etc.). Other candidate capping layer materials that require additional research to address these material challenges include, but are not limited to: a-C:H, CNx, and BCNx, which exhibit low-k (k<3.9), some compatibility with interconnect processing, and the ability to impede Cu diffusion.